Yes, it is. For my nearing-40 frame, my pot belly, and lack of flexibility added to the disk problems, it was exhausting and painful. But, I can see where the benefits lay. If I can somehow force myself to lose 50 more pounds, I'll be back where I should be for my frame, and then I intend to add a 'harder' MA to the regimen... Judo and/or BJJ are the immediates that come to mind. and that ukemi experience will be invaluable in both or either cases, I think.
Yes, I still want to take an art that has practical street use. I think I recall that I'll never be 'good' at it at my age (I believe that BKR told someone else that their age limits how good someone can be, or something immediately similar, IRC), but just being able to become good enough to some day merit shodan would be pretty effin sweet, in my opinion.
(I wish I could understand the promotional points in judo bit... *sigh*)

Most clubs don't require you to wait a year until sparring in kendo. 3-6 months is more typical. The reason is that your basics fall apart when you start wearing armour, so we like to see them at some reasonable level.

There's no dan restriction for competition. Most kendo competitions have divisions for mudansha and then several dan divisions (eg 1-2 dan, 3 dan, 4+ dan). Shodan in kendo is typically only a couple of years of recreational practice anyway, don't get too hung up on the "black belt" thing. It's pretty much an advanced beginner kind of level.

If the OP is still paying attention and has more questions, feel free to ask. But his time might be better spent on the kendo world forums which is the major place that kendo people hang out, net-wise.

ETA just noticed the OP is now a "guest", assuming account deleted. Leaving this answer up for posterity.